The present invention relates to determination of the concentration of specific metabolic acids in biological fluids, and in particular, the concentration of betahydroxybutyrate and lactic acid in biological fluids.
In humans, as well as in certain other animals, the organism may experience or suffer from a state of metabolic acidosis. Of the types of acidosis, there are recognized hyperketonemia, hyperlacticacidemia, uremicacidemia, and toxicacidemia.
On certain occasions, it may be possible to determine that there is present a condition of metabolic acidosis, but determination of the type of acidosis present may be difficult without expensive and time-consuming laboratory analysis. Moreover, it may be difficult to determine even whether there is present a metabolic acidosis condition. For example, with respect to hyperketonemia there is a rapid semi-quantitative test for only one ketone body, namely, acetoacetate. The test for acetoacetate concentration is made by use of a nitroprusside impregnated test surface. The test surface is then immersed in the biological fluid to be assayed, and an indication of the concentration can be obtained by observing the color of the test surface after a predetermined time has elapsed. Disadvantages of the nitroprusside technique are discussed in K. G. M. M. Alberti and T. D. R. Hockaday, "Rapid Blood Ketone Body Estimation in the Diagnosis of Diabetic Ketoacidosis," 1972 British Medical Journal, 2, 565-568. The nitroprusside technique does not measure the concentration of betahydroxybutyrate, the major ketone body. The result is the possibility of a misleading determination of the total ketone bodies in the biological fluids.
Although lactic acidosis may be the most common form of metabolic acidosis, there is a problem in determining rapidly the concentration of lactate in biological fluids. Short of laboratory analysis, it is common for the physician to assume the presence of lactic acidosis when other forms of metabolic acidosis have been ruled out by other techniques. For example, the relatively poor nitroprusside technique is used to rule out the presence of hyperketonemia, and other methods are used to rule out the presence of uremicacidemia and toxicacidemia. Thus, despite the frequency of occurrence of lactic acidosis, the number of cases actually documented on the basis of direct analysis are relatively uncommon.